Alexandre A. Todorov

Meta-analysis of genome-wide association studies of attention-deficit/hyperactivity disorder

OBJECTIVE Although twin and family studies have shown attention-deficit/hyperactivity disorder (ADHD) to be highly heritable, genetic variants influencing the trait at a genome-wide significant level have yet to be identified. As prior genome-wide association studies (GWAS) have not yielded significant results, we conducted a meta-analysis of existing studies to boost statistical power. METHOD We used data from four projects: a) the Childrens Hospital of Philadelphia (CHOP); b) phase I of the International Multicenter ADHD Genetics project (IMAGE); c) phase II of IMAGE (IMAGE II); and d) the Pfizer-funded study from the University of California, Los Angeles, Washington University, and Massachusetts General Hospital (PUWMa). The final sample size consisted of 2,064 trios, 896 cases, and 2,455 controls. For each study, we imputed HapMap single nucleotide polymorphisms, computed association test statistics and transformed them to z-scores, and then combined weighted z-scores in a meta-analysis. RESULTS No genome-wide significant associations were found, although an analysis of candidate genes suggests that they may be involved in the disorder. CONCLUSIONS Given that ADHD is a highly heritable disorder, our negative results suggest that the effects of common ADHD risk variants must, individually, be very small or that other types of variants, e.g., rare ones, account for much of the disorders heritability.

Genome-wide copy number variation study associates metabotropic glutamate receptor gene networks with attention deficit hyperactivity disorder

Attention deficit hyperactivity disorder (ADHD) is a common, heritable neuropsychiatric disorder of unknown etiology. We performed a whole-genome copy number variation (CNV) study on 1,013 cases with ADHD and 4,105 healthy children of European ancestry using 550,000 SNPs. We evaluated statistically significant findings in multiple independent cohorts, with a total of 2,493 cases with ADHD and 9,222 controls of European ancestry, using matched platforms. CNVs affecting metabotropic glutamate receptor genes were enriched across all cohorts (P = 2.1 × 10−9). We saw GRM5 (encoding glutamate receptor, metabotropic 5) deletions in ten cases and one control (P = 1.36 × 10−6). We saw GRM7 deletions in six cases, and we saw GRM8 deletions in eight cases and no controls. GRM1 was duplicated in eight cases. We experimentally validated the observed variants using quantitative RT-PCR. A gene network analysis showed that genes interacting with the genes in the GRM family are enriched for CNVs in ∼10% of the cases (P = 4.38 × 10−10) after correction for occurrence in the controls. We identified rare recurrent CNVs affecting glutamatergic neurotransmission genes that were overrepresented in multiple ADHD cohorts.

Genome-wide analysis of copy number variants in attention deficit hyperactivity disorder: the role of rare variants and duplications at 15q13.3

Objective: Attention deficit hyperactivity disorder (ADHD) is a common, highly heritable psychiatric disorder. Because of its multifactorial etiology, however, identifying the genes involved has been difficult. The authors followed up on recent findings suggesting that rare copy number variants (CNVs) may be important for ADHD etiology. Method: The authors performed a genome-wide analysis of large, rare CNVs (<1% population frequency) in children with ADHD (N=896) and comparison subjects (N=2,455) from the IMAGE II Consortium. Results: The authors observed 1,562 individually rare CNVs >100 kb in size, which segregated into 912 independent loci. Overall, the rate of rare CNVs >100 kb was 1.15 times higher in ADHD case subjects relative to comparison subjects, with duplications spanning known genes showing a 1.2-fold enrichment. In accordance with a previous study, rare CNVs >500 kb showed the greatest enrichment (1.28-fold). CNVs identified in ADHD case subjects were significantly enriched for loci implicated in autism and in schizophrenia. Duplications spanning the CHRNA7 gene at chromosome 15q13.3 were associated with ADHD in single-locus analysis. This finding was consistently replicated in an additional 2,242 ADHD case subjects and 8,552 comparison subjects from four independent cohorts from the United Kingdom, the United States, and Canada. Presence of the duplication at 15q13.3 appeared to be associated with comorbid conduct disorder. Conclusions: These findings support the enrichment of large, rare CNVs in ADHD and implicate duplications at 15q13.3 as a novel risk factor for ADHD. With a frequency of 0.6% in the populations investigated and a relatively large effect size (odds ratio=2.22, 95% confidence interval=1.5–3.6), this locus could be an important contributor to ADHD etiology.

Contributions of parental alcoholism, prenatal substance exposure, and genetic transmission to child ADHD risk: a female twin study

BACKGROUND Genetic influences have been shown to play a major role in determining the risk of attention-deficit hyperactivity disorder (ADHD). In addition, prenatal exposure to nicotine and/or alcohol has also been suggested to increase risk of the disorder. Little attention, however, has been directed to investigating the roles of genetic transmission and prenatal exposure simultaneously. METHOD Diagnostic telephone interview data from parents of Missouri adolescent female twin pairs born during 1975-1985 were analyzed. Logistic regression models were fitted to interview data from a total of 1936 twin pairs (1091 MZ and 845 DZ pairs) to determine the relative contributions of parental smoking and drinking behavior (both during and outside of pregnancy) as risk factors for DSM-IV ADHD. Structural equation models were fitted to determine the extent of residual genetic and environmental influences on ADHD risk while controlling for effects of prenatal and parental predictors on risk. RESULTS ADHD was more likely to be diagnosed in girls whose mothers or fathers were alcohol dependent, whose mothers reported heavy alcohol use during pregnancy, and in those with low birth weight. Controlling for other risk factors, risk was not significantly increased in those whose mothers smoked during pregnancy. After allowing for effects of prenatal and childhood predictors, 86% of the residual variance in ADHD risk was attributable to genetic effects and 14% to non-shared environmental influences. CONCLUSIONS Prenatal and parental risk factors may not be important mediators of influences on risk with much of the association between these variables and ADHD appearing to be indirect.

Methylation at SLC6A4 is linked to family history of child abuse: An examination of the Iowa Adoptee sample

In this letter we describe novel, preliminary work, examining a possible mechanism of the Gene-environment interactions thought to moderate the response of individuals to stressful life events. The molecular mechanisms through which this moderation may be accomplished are currently unknown but some have suggested DNA methylation (Lui and others, 1997; McGowan and others 2009). In order to test this hypothesis, we analyzed the relationship of child abuse to methylation of cytosine residues in the promoter region of the serotonin transporter gene in DNA from 96 male and 96 female subjects from the Iowa Adoptee Studies using a principal components analysis. The results from this preliminary work suggest a lasting effect of child abuse on overall methylation levels in both males and females.

Methylation at 5HTT Mediates the Impact of Child Sex Abuse on Women's Antisocial Behavior: An Examination of the Iowa Adoptee Sample

Objective: To examine epigenetic processes linking childhood sex abuse to symptoms of antisocial personality disorder (ASPD) in adulthood and to investigate the possibility that the link between childhood sex abuse and deoxyribonucleic acid methylation at the 5HTT promoter might represent a pathway of long-term impact on symptoms of ASPD. Method: Deoxyribonucleic acid was prepared from lymphoblast cell lines derived from 155 female participants in the latest wave of the Iowa Adoptee Study. Methylation at 71 CpG residues was determined by quantitative mass spectroscopy, and the resulting values were averaged to produce an average CpG ratio for each participant. Simple associations and path analyses within an Mplus framework were examined to characterize the relationships among childhood sex abuse, overall level of methylation among women, and subsequent antisocial behavior in adulthood. Direct effects of biological parent psychopathology and 5HTT genotype were controlled. Results: Replicating prior work, we found that a significant effect of childhood sex abuse on methylation of the 5HTT promoter region emerged for women. In addition, a significant effect of methylation at 5HTT on symptoms of ASPD emerged. Conclusions: Child sex abuse may create long-lasting changes in methylation of the promoter region of 5HTT in women. Furthermore, hypermethylation may be one mechanism linking childhood sex abuse to changes in risk for adult antisocial behavior in women. Better understanding of the methylome may prove critical in understanding the role of childhood environments on long-term psychiatric sequelae. 5HTT = serotonin transporter gene; CpG = a site at which cytosine (C) lies next to guanine (G) in the deoxyribonucleic acid sequence; ASPD = antisocial personality disorder.

Resiliency factors protecting against teenage alcohol use and smoking: influences of religion, religious involvement and values, and ethnicity in the Missouri Adolescent Female Twin Study.

The objective of this study was to investigate the contribution of ethnicity (African American vs European/other ancestry), family religious affiliation, religious involvement, and religious values, to risk of alcohol and cigarette use in adolescent girls; and to estimate genetic and shared environmental effects on religious involvement and values. Telephone interviews were conducted with a sample of female like-sex twin pairs, aged 13-20 (n = 1687 pairs, including 220 minority pairs), as well as with one or both parents of twins aged 11-20 (n = 2111 families). These data, together with one-year follow-up twin questionnaire data, and two-year follow-up parent interview data, were used to compare ethnic differences. Proportional hazards regression models and genetic variance component models were fitted to the data. Despite higher levels of exposure to family, school and neighborhood environmental adversities, African American adolescents were less likely to become teenage drinkers or smokers. They showed greater religious involvement (frequency of attendance at religious services) and stronger religious values (eg belief in relying upon their religious beliefs to guide day-to-day living). Controlling for religious affiliation, involvement and values removed the ethnic difference in alcohol use, but had no effect on the difference in rates of smoking. Religious involvement and values exhibited high heritability in African Americans, but only modest heritability in EOAs. The strong protective effect of adolescent religious involvement and values, and its contribution to lower rates of African American alcohol use, was confirmed. We speculate about the possible association between high heritability of African American religious behavior and an accelerated maturation of religious values during adolescence.

Family-Based Genome-Wide Association Scan of Attention-Deficit/Hyperactivity Disorder

OBJECTIVE Genes likely play a substantial role in the etiology of attention-deficit/hyperactivity disorder (ADHD). However, the genetic architecture of the disorder is unknown, and prior genome-wide association studies (GWAS) have not identified a genome-wide significant association. We have conducted a third, independent, multisite GWAS of DSM-IV-TR ADHD. METHOD Families were ascertained at Massachusetts General Hospital (MGH; N = 309 trios), Washington University at St. Louis (WASH-U; N = 272 trios), and University of California at Los Angeles (UCLA; N = 156 trios). Genotyping was conducted with the Illumina Human1M or Human1M-Duo BeadChip platforms. After applying quality control filters, association with ADHD was tested with 835,136 SNPs in 735 DSM-IV ADHD trios from 732 families. RESULTS Our smallest p value (6.7E-07) did not reach the threshold for genome-wide statistical significance (5.0E-08), but one of the 20 most significant associations was located in a candidate gene of interest for ADHD (SLC9A9, rs9810857, p = 6.4E-6). We also conducted gene-based tests of candidate genes identified in the literature and found additional evidence of association with SLC9A9. CONCLUSIONS We and our colleagues in the Psychiatric GWAS Consortium are working to pool together GWAS samples to establish the large data sets needed to follow-up on these results and to identify genes for ADHD and other disorders.

Co-morbid pain and psychopathology in males and females admitted to treatment for opioid analgesic abuse.

Abstract The purpose of this study was to identify co‐morbidity in a national sample (N = 1408) of males and females entering treatment for opioid abuse. Our sample was primarily white, lived in small urban, suburban or rural locations (80%), and was well‐educated. Chronic pain was a symptomatic feature in over 60% of all subjects. Furthermore, 79% of male and 85% of female prescription opioid abusers indicated that their first exposure to an opioid was a legitimate prescription for pain which subsequently led 60–70% to misuse to get high. Our data also indicate that the use of prescription opioids to get high represents the end stage on a continuum of substance abuse, beginning at a very early age. The age of first alcohol use, getting drunk, smoking, use of marijuana, stimulants and other non‐opioid prescription or illicit drugs occurred very early (13–19) in prescription opioid misusers/abusers, whose first use of opioids did not occur, on average, until age 22. Finally, most of the sample had sought treatment 3 or more times for substance abuse prior to the treatment admission in which the survey was completed. Physical and mental health were very poor in both male and female prescription opioid abusers, but females were more ill and dysfunctional than males in all physical and particularly emotional domains. Our results suggest that a small number of “at risk” opioid naive pain patients, who might abuse their therapeutically appropriate opioid analgesics, can be identified by assessing pre‐ and co‐morbid substance abuse and significant psychopathology.

Genetic Linkage to Chromosome 22q12 for a Heavy-Smoking Quantitative Trait in Two Independent Samples

We conducted a genomewide linkage screen of a simple heavy-smoking quantitative trait, the maximum number of cigarettes smoked in a 24-h period, using two independent samples: 289 Australian and 155 Finnish nuclear multiplex families, all of which were of European ancestry and were targeted for DNA analysis by use of probands with a heavy-smoking phenotype. We analyzed the trait, using a regression of identity-by-descent allele sharing on the sum and difference of the trait values for relative pairs. Suggestive linkage was detected on chromosome 22 at 27-29 cM in each sample, with a LOD score of 5.98 at 26.96 cM in the combined sample. After additional markers were used to localize the signal, the LOD score was 5.21 at 25.46 cM. To assess the statistical significance of the LOD score in the combined sample, 1,000 simulated genomewide screens were conducted, resulting in an empirical P value of .006 for the LOD score of 5.21. This linkage signal is driven mainly by the microsatellite marker D22S315 (22.59 cM), which had a single-point LOD score of 5.41 in the combined sample and an empirical P value <.001 from 1,000 simulated genomewide screens. This marker is located within an intron of the gene ADRBK2, encoding the beta-adrenergic receptor kinase 2. Fine mapping of this linkage region may reveal variants contributing to heaviness of smoking, which will lead to a better understanding of the genetic mechanisms underlying nicotine dependence.